1. Field of the Invention
The present invention relates to a Q-switch laser device, and in particular, the Q-switch laser device for generating a laser wave of a peak shape by applying an RF (Radio Frequency) signal to a Q-switch and modulating the RF signal.
2. Description of the Related Art
Conventionally, a Q-switch laser device is widely utilized in a precision processing such as cutting, punching, and marking of a material by instantaneously taking out energy (unit J, joule) accumulated inside an optical resonator as a laser light, which has extremely high peak power (unit W, watt), with using an optical means called a Q-switch.
Referring FIGS. 9 and 10, a configuration and principle of a drive unit in a conventional Q-switch laser device will be described. FIG. 9 is a block diagram showing a basic configuration of the drive unit for driving a Q-switch in the conventional Q-switch laser device. FIG. 10 is an illustration drawing representing signals which components configuring the drive unit handle.
A drive unit 30C consists of an RF oscillator 31′, a switch pulse generator 32′, and an RF modulation circuit 35′.
The RF oscillator 31′ oscillates, for example, an RF signal of 40 MHz as shown in FIG. 10. The RF signal is a signal for operating a Q-switch not shown so that a Q-value becomes a low value when the RF signal is input to an optical resonator 20′. The switch pulse generator 32′ generates a switch pulse (SP signal) (FIG. 10) having, for example, a frequency of 5 kHz. A repetition frequency of the SP signal, that is, a period thereof determines a repetition period of laser waves 25a′ of a peak shape output from the optical resonator 20′. The RF modulation circuit 35 modulates the RF signal corresponding to periods of an L-level and H-level of the SP signal and generates an RF modulation signal (FIG. 10).
Because if inputting the RF modulation signal (FIG. 10) to the not shown Q-switch arranged inside the optical resonator 20′, a resonator loss increases (the Q-value becomes the low value) when the RF modulation signal is ON, a stimulated emission is suppressed inside the optical resonator 20′ and thereby a laser oscillation results in stopping a generation thereof. And when the RF modulation signal is OFF, the resonator loss decreases (the Q-value becomes a high value). After a constant delay time, when the RF modulation signal changes from ON to OFF, lapses, the laser waves 25a′ of the peak shape are output as a continual pulse laser (for example, see paraphrases 0020 to 0100 and FIGS. 4, 10, and 11 in Japanese Patent Laid-Open Publication 2000-101176 and paraphrases 0002 to 0006 and FIG. 6 in Japanese Patent Laid-Open Publication 2002-359422).
However, in the conventional Q-switch laser device thus described the RF signal and the SP signal are generated from the RF oscillator 31′ and the switch pulse generator 32′, respectively, and are independent signals. Therefore, as shown in enlarged partial drawings (a), (b), and (c) of FIG. 10, each phase of the RF modulation signal at arising timing thereof to the H-level does not accord with any phase. Thus a waveform at timing when the RF modulation signal changes to OFF (the Q-value changes from a low value to a high one) has an unstable form. Accordingly, because an identity of the waveform at a termination portion of an ON period of the RF modulation signal, occurs a phenomenon that an identity is not kept also in the laser waves 25a′ emitted from the optical resonator 20′. Thus deriving from phases of the RF signal and SP signal, which become a basis for generating the RF modulation signal, being not in synchronization, the identity of the laser waves 25a′ is not kept, a jitter increases, and thereby peak power and energy result in fluctuating. Using such the pulse laser, for example, in performing marking and a minuscule processing there is a problem that a predetermined shape cannot be maintained.
On the other hand, as in an invention in Japanese Patent Laid-Open Publication 2001-7429, for such the problem is proposed a method for aligning the phase of the RF signal at an arising position of a trigger pulse applied to these Q-switch lasers. But because in this invention a concrete circuit for controlling an OFF phase of the RF signal is not proposed, a pulse laser control by a gate signal is required for a laser output, and a pulse distance of a pulse laser is not fixed, it is thought that a realization thereof is not easy.
Thus in order to solve the problem described above, it is strongly requested to provide a Q-switch laser device with no jitter whose output is stable by mounting a simple circuit for synchronizing the phase of the RF signal with that of the SP signal for modulating the RF signal.